Triploid interspecific hybrid flowering pear tree named ‘NCPX2’

ABSTRACT

‘NCPX2’ is a new triploid, interspecific hybrid flowering pear with a broadly pyramidal habit, white flowers, multi-coloured fall foliage, resistance to fire blight, and significantly reduced fertility.

Latin name of the genus and species: The Latin name of the novel plantvariety disclosed herein is Pyrus x triploida.

Variety denomination: The inventive triploid, interspecific hybrid ofPyrus calleryana (tetraploid) x Pyrus ‘Silver Ball’ (diploid hybrid)disclosed herein has been given the varietal denomination ‘NCPX2’.

BACKGROUND OF THE INVENTION

The present invention comprises a new and distinct hybrid flowering pearcultivar hereinafter referred to by the cultivar name ‘NCPX2’. This newflowering pear was developed through a breeding program in Mills River,N.C. ‘NCPX2’ was selected from an F₁ population of seedlings grown froma controlled cross of an induced tetraploid Pyrus calleryana(H2002-031-010) (female parent; unpatented) x Pyrus ‘Silver Ball’(diploid hybrid) (male parent; unpatented). The first asexualpropagation of ‘NCPX2’ was carried out in August 2010 by budding inMills River, N.C. and has been asexually reproduced repeatedly bybudding over a 5-year period. ‘NCPX2’ propagates readily from buddingusing chip budding in mid-summer. ‘NCPX2’ has been found to retain itsdistinctive characteristics through successive asexual propagations.

SUMMARY OF THE INVENTION

The following are the unique and distinguishing characteristics of thisnew cultivar when grown under standard horticultural practices in MillsRiver, N.C.

-   -   1. Triploid selection with greatly reduced fertility.    -   2. An upright, pyramidal form with white flowers.    -   3. Resistance to fire blight.    -   4. Showy fall foliage color.

BRIEF DESCRIPTION OF THE PHOTOGRAPHS

This new flowering pear is illustrated by the accompanying photographswhich show the plant's form, foliage and inflorescences. The colorsshown are as true as can be reasonably obtained by conventionalphotographic procedures. Colors in the photographs may differ slightlyfrom the color values cited in the detailed botanical description, whichaccurately describe the colors of the new pear.

FIG. 1 is a photograph demonstrating the upright pyramidal form of aneight year old tree of ‘NCPX2’.

FIG. 2 is a photograph showing the white flowers from an eight year oldtree of ‘NCPX2’.

FIG. 3 is a photograph showing fall foliage colors of a nine year oldtree of ‘NCPX2’.

DETAILED BOTANICAL DESCRIPTION

The following is a detailed description of the botanical characteristicsof the new and distinct variety of interspecific hybrid flowering pearknown by the denomination ‘NCPX2’. The detailed description was taken onthe original nine-year-old tree growing in Mills River, N.C. All colorscited herein refer to The Royal Horticultural Society Colour Chart (TheRoyal Horticultural Society (R.H.S.), London, 2015, 6th Edition). Wherespecific dimensions, sizes, colors, and other characteristics are given,it is to be understood that such characteristics are approximations oraverages set forth as accurately as practicable.

TECHNICAL DESCRIPTION OF THE VARIETY

-   Classification:    -   -   Botanical name.—Pyrus x triploida ‘NCPX2’.        -   Common name.—Triploid hybrid flowering pear.-   Parentage: F₁ hybrid of Pyrus calleryana H2002-031-010 (tetraploid)    x Pyrus ‘Silver Ball’ (diploid interspecific hybrid of uncertain    parentage, possibly P. fauriei x P. betulaefolia).-   Plant description:    -   -   Growth habit.—Upright pyramidal. Height: 8 m after 9 years.            Width: 6 m after 9 years.        -   Shoots and stems.—Branching habit: Upright spreading.            Lateral branch length: 3 to 6 m. Diameter: 3 to 9 cm.            Internode length: 2 to 5 cm. Color: Brown (N200B). Trunk            texture: Smooth to rough. Trunk color: Brown (N200C to            N200D).        -   Mature leaves.—Type: Simple. Persistence: Deciduous.            Arrangement: Alternate. Shape: Ovate. Apex: Acuminate. Base:            Rounded. Venation: Pinnate. Margin: Serrulate. Texture:            Glabrous both upper and lower.        -   Emerging leaves.—Color: Upper surface: Yellow-Green (146A).            Lower surface: Yellow-Green (146B).        -   Mature leaves during growing season.—Color: Upper: Green            (137A). Lower: Yellow-Green (146B). Length of lamina: Avg.            6.1 cm (range 5.5 to 7.0 cm). Width: Avg. 4.6 cm (range 3.5            to 5.0 cm). Petiole: Length: Avg. 3.0 cm (range 2.5 to 4.0            cm). Width: 0.1 cm. Color: Yellow-Green (146D).        -   Mature leaves, fall color.—Variable. Including Brilliant            Orange Yellow (21B), Vivid Red (46C), and Deep Red (53A).        -   Inflorescence.—Bud length: 0.5-0.6 cm. Bud diameter:            0.8-1.0 cm. Bud shape: Ovate. Bud color: Green-White (157C)            with Red-Purple (63C) on tip.        -   Individual flowers.—Diameter: 1.5-2.0 cm. Depth: 0.6-0.8 cm.            Stamen: Number: 19-22. Anther color: Red-Purple (63A).            Filament color: Green-White (157D). Pistil: Number: 2.            Stigma: Shape: Rounded. Color: Greyed-Green (193A). Style:            Length: 0.5-0.6 cm. Color: Yellow-Green (144D). Ovary color:            Green (138A). Petals: Arrangement: Star. Number: 5 petals.            Shape: Elliptic. Margin: Entire. Tip: Obtuse. Length (at            anthesis): 0.8-1.0 cm. Width (at anthesis): 0.7-0.9 cm.            Color when opening: Green-White (157D). Color fully opened:            White (NN155C).        -   Fruit.—Pome: 4 locules. Size: 0.5-1.0 in. diameter. Shape:            Round to ovoid. Color: Gray orange to gray brown (including            177B, N199B, N199D). Lenticels: Many small, circular on            surface. Calyx: Mostly deciduous. Length: 0.1-0.11 in.            Diameter: 0.08-0.1 in. Pedicel: Length: 0.55-1 in. Diameter:            0.03-0.05 in. Color: Green (132B).-   Disease and insect resistance: No significant disease or insect    pests have been observed. ‘NCPX2’ was found to have a high level of    resistance to fire blight (see data below).-   Cold hardiness: At least USDA zone 5b; testing has not been    completed in colder zones.-   Nomenclature: To help clarify the nomenclature of Pyrus spp.    hybrids, nothospecies Pyrus x triploida Ranney is proposed for the    hybrid species name in accordance with Article H.3-5 (McNeill et    al., 2012). The new hybrid species is described as follows:    Nothospecies Pyrus x triploida Ranney, a triploid, interspecific    hybrid between Pyrus calleryana Decne. and another Pyrus L. species    or hybrid. Primary diagnostic characteristics are a 2C holoploid    relative genome size of approximately 1.88±0.12 (Standard Error) pg    reflecting an intermediate triploid between tetraploid 2.63±0.06    (SE) pg and diploid 1.25±0.05 (SE) pg parents (Following methods of    Phillips et al., 2016).-   Typification: Pyrus x triploida Ranney, nothosp. nov.-   Type: United States, N.C., Mills River, 2C relative genome size of    1.93 pg, 8 m tall, 6 m wide, upright pyramidal form, NCSU    H2008-049-145, 11 Nov. 2017, Ranney MCIL 2017-001 (holotype: NCSC,    here designated; isotype NA).

MOPHOLOGICAL COMPARISONS WITH OTHER TAXA

A comparison of morphological characteristics between ‘NCPX2’ and othercommercial flowering pear cultivars is presented in Table 1.

TABLE 1 Morphological comparison of ‘NCPX2’ with other commercialflowering pear cultivars Cultivars Pyrus Pyrus calleryana Pyrus ‘NCPX1’Pyrus ‘Cleveland pyrifolia (U.S. ‘Silver Select’ ‘Ohara Plant Ball’(unpat- Beni’ Pat. No. Pyrus (unpat- Trait ented) (unpatented) 26,539)‘NCPX2’ ented) Tree Upright Upright Very Upright Compact, growthpyramidal columner. narrow pyramidal round, Habit fastigate dwarf Tree 8m 8 m 8 m 8 m 4 m Height (after 8 years) Tree 6 m 5 m 2m 6 m 4 m Width(after 8 years) Flower White Red Red Green- Green- bud (N155A) purplepurple white White color (53C to (53C to (157C) (157B) 63A) 63A) withRed- Purple (63C) on tip. Flower White White White Green- Green petal(N155A) (N155A) (N155A) White white color with some with some (157D)(157D) when pink blush pink blush opening (63A, (63A, 58C, and 58C, and65A) 65A) Flower White White White/ White White petal (N155A), (N155A),pink (NN155C) (N155) color (155B) when fully opened Flower 1.0 to 2.5 to3.1 to 1.5-2.0 cm 1.0 to diameter 2.0 cm 3.3 cm 3.6 cm 2.5 cm

FIRE BLIGHT RESISTANCE

Disease resistance to fire blight was evaluated following the proceduresof Bell et al, (2004). Briefly, a virulent strain of Erwinia amylovora(E2002a) was prepared from 24 hour old cultures grown on nutrient agar.Three actively growing shoots were inoculated in May 2012 by bisectingthe youngest leaves with a pair of scissors that had been dipped intothe inoculum prior to each cut. The disease lesion length and totallength of the current season's growth of the inoculated shoot weremeasured 40 days following inoculation. The severity of infection wasexpressed as the length of the fire blight lesion as a percentage ofoverall shoot length. ‘NCPX2’ was found to have a high level ofresistance to fire blight with a mean lesion length of 0.8% followingcontrolled inoculations (Table 2). No signs or symptoms of fire blighthave been observed on ‘NCPX2’ as the result of natural infection overthe last 8 years.

TABLE 2 Comparison of tire blight resistance among ‘NCPX2’ and othercommercial flowering pear Cultivars. Disease severity - 2012 (% lesionlength) Cultivar Range Mean. ‘Ohara Beni’ 100-100 100 ‘Cleveland Select’ 0-20 6.6 ‘NCPX1’ 0-0 0.0 ‘NCPX2’ 0-3 0.8

REPRODUCTIVE CHARACTERISTICS

Female fertility of selected triploid pears, including ‘NCPX2’(H2008-049-145) was evaluated and published by Phillips et al. (2016)with a summary presented in Table 3. Female fertility was characterizedby evaluating fruit set, seeds per fruit, seed germination, seedlingsper flower, and percent relative fertility [(seedlings per flower fortriploid/seedlings per flower for diploid control)×100], outdoors withfavorable cross pollination conditions. Flow cytometry was used todetermine relative genome sizes and ploidy levels. Relative fertility of‘NCPX2’ was 0.86% of the most fertile diploid control, a reduction of99.14%. Furthermore, the limited seedlings that did germinate fromtriploids maternal parents, including ‘NCPX2’, were determined to beprimarily abnormal aneuploids with non-standard chromosome numbers.

TABLE 3 Ploidy, relative 2C genome size, and fertility characteristicsfor ‘NCPX2’ and selected diploids as published by Phillips et al.(2016). Rela- tive Re- gen- Ger- lative ome Fruit min- Seed- fertil-Ploidy size set Seeds/ ation lings/ ity^(Z) Selection (X) (pg) (%) fruit(%) flower (%) ‘NCPX2’ 3 1.93 ± 3.46 ± 2.05 ± 5.22 ± 0.01 ± 0.86 (H2008-0.01 0.07 3.48 0.11 0.01 049-145) Diploid 1 2 1.26 ± 9.80 3.89 ± 38.610.13 ± 16.73 0.02 ± 2.93 ± 0.08 0.07 0.11 Diploid 2 2 1.22 ± 11.06 3.24± 25.45 0.13 ± 16.3 0.01 ± 0.51 ± 0.35 0.11 0.49 Diploid 3 2 1.23 ±46.76 3.16 ± 52.83 0.80 ± 100.00 0.01 ± 0.72 ± 0.62 0.22 0.15^(Z)Calculated as (seedlings/flower)/(0.80), where 0.80 is the number ofseedlings per flower of the most fertile diploid eontrol,

‘NCPX2’ is distinguished from other flowering pear cultivars by itsunique combination of traits including a triploid cytotype with a 2Cgenome size of approximately 1.93 pg, an upright pyramidal form, whiteflower petals, high resistance to fire blight, and low female fertility.

CITATIONS

-   Bell, A. C., T. G. Ranney, and T. A. Eaker. 2004. Resistance to fire    blight among flowering pears and quince. HortScience 40(2):413-415.-   McNeill, J., F. R. Barrie, W. R. Buck, V. Demoulin, W.    Greuter, D. L. Hawksworth, P. S. Herendeen, S. Knapp, K. Marhold, J.    Prado, W. F. Rrud'homme Van Reine, G. F. Smith, J. H. Wiersema,    and N. J. Turland. 2012. International code of botanical    nomenclature for algae, fungi, and plants (Melbourne Code). Költz    Sci. Books, Oberreifenberg, Germany.-   Phillips, W. D., T. G. Ranney, D. H. Touchell, and T. A.    Eaker. 2016. Fertility and reproductive pathways of triploid    flowering pears (Pyrus sp.). HortScience 51(8):968-971.

What is claimed is:
 1. A new and distinct triploid, interspecific hybridflowering pear tree named ‘NCPX2’ as illustrated and described herein.